Variable-speed electric motor.



E. ROSENBERG.

VARIABLE SPEED ELECTRIC MOTOR. APPLICATION HLED 001.9.1911.

1,222,469. Patented Apr. 10, 1917.

Y mluggm m 2.

Big. 6.

WITNESSES; E19. 6'. INVENTOR 7 ATTORNEY ED STATES PATENT OFFICE.

EMANUEL ROSENBERG, OF ALTRINCI-IAM, ENGLAND, ASSIGNOR T WESTINGHOUSEELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

VARIABLE-SPEED ELECTRIC MOTOR.

Application filed October 9, 1911.

To all whom it may concern:

a subject of the Emperor of Austria, and a resident of Altrincham, inthe county of Chester, England, have invented a new and usefulImprovement in Variable-Speed Electric Motors, of which the following isa specification.

My invention relates to direct current motors and more particularly tomotors that are adapted to have considerable ranges of speed withcomparatively small variations in the amounts of current suppliedthereto, the speeds increasing as the supply of current to the motors isreduced and vice versa. Motors of the kind above mentioned, the rotorsof which are provided with flywheels, are employed in order to effectequalization of the loads on the supply circuits to which the motors areconnected, energy being stored in the fly-wheels in the form of kineticenergy when the loads on the supply circuits are low, the energy thusstored being discharged in the formof mechanical energy to assist themotors in driving the loads, or in the form of electrical energy, inwhich case the motors are driven as generators by the fly-wheels todischarge into the supply circuits when the loads on'the latter arehigh.

In order to render the equalizing action of a fly-wheel employed in theabove noted manner as efiective as possible, it is evidently desirablethat a comparatively small differencein the current supplied to themotor should effect a considerable difference in its speed but, on theother hand, even when the motor is only taking a very small amount ofcurrent from the supply circuit, the speed of the motor should notexceed a predetermined limit.

It has previously been proposed to employ a motor of the series type forthe purpose noted and to provide a speed governor to be operated bycentrifugal action or otherwise in such manner as to open acircuitbreaker and thus disconnect the motor from the supply circuitwhen its speed reaches a predetermined limit, or, in some cases, thespeed governor has been arranged to close the circuit of a shunt fieldwinding of the motor in order to maintain a shunt field excitation whichis sufficient to prevent excessive motor s eed, even at the smallestseries excitation o the motor. Such an arrange- Speeification of LettersPatent.

Serial No. 653,714.

ment has, however, the disadvantage of causing a sudden change in theexcitation of the motor when the shunt field winding be comes operative,a further disadvantage being due to the fact that an electro-mechanicalapparatus is necessary for actuating the circuit-breaker for the shuntfield winding. A somewhat complicated apparatus is also required to cutout the shunt winding at the proper moment when the speed is at a lowervalue and the main current has increased.

On the other hand, if a compound wound motor be employed, the shuntfield Winding of which is sufficient to prevent the motor from attainingan excessive speed, even when very small amounts of current are suppliedto the motor, the disadvantage exists that the shunt field windingreduces considerably the influence of the series field excitation at lowspeeds and, consequently, the efficiency of the equalizing effect on thefly- Wheel.

According to the present invention, a compound-wound motor is employed,the shunt field winding of which is excited by current which is variedin accordance with the speed of the motor, so that, at low speeds, thecharacteristic of the motor resembles very closely that of a seriesmotor and, at high speeds, it resembles that of a shunt motor.

In order that the invention may be clearly understood, it will now bedescribed with reference to the accompanying drawings in which Figure 1is a diagram illustrating one method of carrying out the invention inpractice. Fig. 2 is a diagram of curves relating to the motor shown inFig. 1. Figs. 3 and l are diagrams similar to Figs. 1 and 2,respectively, and illustrating another method of carrying out theinvention. Fig. 5 is a diagram illustrating a further modification ofthe invention, and Fig. 6 is a diagram illustrating anothermodification.

Referring now to Fig. 1, the armature 1 of the motor is supplied fromthe leads 2 and 3 with direct current which also passes through theseries field magnet winding 4; of the motor. The shunt field magnetwinding 5. of the motor is supplied with current from an exciter, thearmature 6 of which is mounted on the shaft of the armature 1. The fieldmagnet 7 of the exciter is supplied with current from a source ofconstant voltage, such as the battery 8. It will be ob- Patented Apr.10, 1917.

vious that the current in the shunt field winding 5 of the motor will beapproximately proportional to the speed of the motor.

In Fig. 2, three curves are shown, the ordinates measured along the axisOY representing ampere turns and the abscissae measured along the axisOX representing revolutions per minute. Curve a shows the relationshipbetween the total number of ampere turns on the field magnet of themotor and the speed of the same. It the motor were a simple series motorthe ordinates of the curve a would also represent, on another scale, thecurrent taken by the motor in amperes. Curve Z) represents the ampereturns of the shunt winding 5 at difi'erent speeds, and the difference ofthese two curves, which is shown by the curve 0, represents the ampereturns or" the series field winding 4i for difierent speeds. It will beobserved that the curve C cuts the axis OK at the point P, which showsthat, even when the current supplied to the motor from the leads 2 and 3falls to zero, the speed does not rise above that represented by theabscissa OP.

Referring now to Fig. 3, the arrangements are similar to those shown inFig. 1, but the field magnet winding 7 of the exciter is connectedacross the terminals or the armature 6 in place of being energized froma source of constant voltage, that is to say, the exciter is an ordinaryshunt wound machine. In this case, the shunt field excitation of themotor will increase or decrease at a much greater rate than the speed,so long as the field of the exciter is magnetically unsaturated. Theshunt field excitation of the motor thus increases very rapidly as themotor reaches its maximum speed but will be extremely small throughoutthe greater part of the range of speed until a value is reached which isnear the permissible limit. These conditions are illustrated in thecurves shown in Fig. Al, which are somewhat similar to those of Fig. 2.In this case, however, the curve 6, which shows the relationship betweenthe ampere turns of the fieldmagnet winding 5 and the speed of themotor, turns up rapidly at the end. It will be noted that the curve 0 isvery similar to the curve a at low speeds but, when the speed rises tonear the desired limit, it suddenly turns down and cuts the axis ofabscissae at the point P. This shows that the speed of the motor willvary very rapidly with the current supplied from the leads 2 and 3 whenthis is low.

As will be readily understood, the arrangement above described may bemodified by providing the motor, in addition to the variable shuntexcitation, with a third field winding and supplying it with currentfrom a source of approximately constant voltage,

such, for instance, as the supply circuit itself,

the effect of this additional field winding being to provide a shuntfield excitatlon for F 5 is a diagram illustrating a motor having itsshunt field winding excited as shown in Fig. 2 and employed for thispurpose. A further modification is also illustrated in that the seriesfield winding i is connected across a resistance 8 which carries thecurrent from the generating station, represented in the diagram by thegenerator 9, and a third field winding 5 is connected across thegenerator circuit. The main current is supplied through mains 10 and 11to a variable load such as motors for operating hoists. r 1 fiy-wheel 12is mounted on the shaft of the armature l and exciter armature 6. Thecurves shown in Fig. a will represent the characteristics of the motor,the curve 0 showing the relationship between the current in the fieldwinding a and the speed of the motor, which is of course the speed ofthe fly-wheel and, on a different scale, represents the current suppliedfrom the gen erating station. If it is assumed that the speed of thefly-wheel is desired to vary between the speeds n and n Fig. 4, thevariation in current supplied by the generating station will berepresented by the ordinates n N 91 N The current in fact does not varyvery greatly from the average current which is given by the value of theordinate at the point N. The armature 1 will obviously take suificientcurrent from the mains 10 and 11 when the line voltage exceeds that ofthe armature, to bring the armature up to the corresponding speed ordeliver suliicient current thereto to supply the difference between amomentary demand on the hoist motor and the current supplied by thegenerating station when the line voltage falls below that of thearmature.

In Fig. 6 is illustrated a system that differs from that shown in Fig. 5only in utilizing a single coil 5 in place of the coils 5 and 5 andsupplying energizing currents to this coil from the line conductors 10and 11 and the exciter 6 connected in parallel re lation, it beingunderstood that the circuit 1011 represents any source of approximatelyconstant voltage.

The invention may be utilized in connection with motors for operatingrolling mills or for other cases in which the motor loads are veryvariable and, as will be seen from an inspection of the curve 0 in Fig.4;, it may be utilized to obtain a considerable reduction in motorspeeds when an increase in the current supplied thereto occurs. In

all of the forms of the invention, the series field winding of the motormay, if desired, be connected in the supply circuit or across theterminals of a resistance in the supply circuit, as illustrated in Fig.5, instead of being connected in series with the motor armature.

The exciter armature may be connected to the motor by any suitablegearing in place of being mounted upon the same shaft.

I claim as my invention:

1. The combination with a compound wound direct current motor, of anexciter for one of the windings of said motor, the speed of which varieswith that of the motor and which is itself excited by current from awinding connected as a shunt to its armature.

2. The combination with a direct current motor having a series fieldmagnet winding, a winding supplied with current from a source ofconstant voltage, and a third winding of an eXciter for said thirdWinding the speed of which varies with that of the motor and Which isitself excited by current from a winding connected as a shunt to itsarmature.

3. The combination with a direct current motor having a plurality offield magnet windings, one of which is in series relation to itsarmature, of an eXciter for another of said field magnet windings, thespeed of which varies with that of the motor and which is itself excitedby current from a Copies of this patent may be obtained for five centseach, by addressing the Commissioner of Patents,

- of the field windings of the motor that has a field winding connectedas a shunt to its armature and the speed of which varies with that ofthe motor.

6. The combination with a direct current motor having a series fieldwinding, a winding supplied with current from a source of constantvoltage and a third winding arranged to aid said series field winding,of an exciter for said third winding, the speed of which varies withthat of the motor and which is itself excited by current from a windingconnected as a shunt to its armature.

In testimony whereof, I have hereunto subscribed my name this nineteenthday of September, 1911.

EMANUEL ROSENBERG.

Witnesses:

NORMAN H. SHEARD, JAs. STEWART BROADFOOT.

Washington, D. 0.

